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Abstract:

A method for voltage regulation, control, protection and monitoring of
state of on-load tap changers of power transformers, voltage regulators,
and capacitor banks comprising: uses a voltage regulation system that has
sets of voltage regulation parameters available for programming by a
user. Each of these sets is adjustable in an independent manner for a
given prevailing load condition. The parameters include a desired rated
voltage at a load; a voltage variance percentage allowed over and below
rated voltage; time delay adjustments for CDC (15) actuation in order to
correct voltage; choice of linear or reverse time delay type; and
parameters referring to voltage drop in the line.

Claims:

1. A METHOD FOR VOLTAGE REGULATION, CONTROL, PROTECTION AND MONITORING OF
STATE OF ON-LOAD TAP CHANGERS OF POWER TRANSFORMERS, VOLTAGE REGULATORS,
AND CAPACITOR BANKS comprising: using a voltage regulation system (S)
that has six or more sets (20A, 20B, 20C) of voltage regulation
parameters (21) available for programming by a user, each of these sets
(20A, 20B, 20C) being adjustable in an independent manner for a given
prevailing load (L) condition, each set being the parameters (21), and
wherein the parameters comprise: a desired rated voltage at a load; a
voltage variance percentage allowed over and below rated voltage; time
delay adjustments for CDC (15) actuation in order to correct voltage;
choice of linear or reverse time delay type; and parameters referring to
voltage drop in the line.

2. The method of claim 1 wherein a selection of the set (20A, 20B, 20C)
of voltage regulation parameters (21) is made by a dry contact input (5),
wherein the selection of the set (20A, 20B, 20C) of voltage regulation
parameters (21) is determined by a combination of open and closed
contacts (5A, 5B, 5C) connected to the dry contact input (5).

3. The method of claim 2, wherein the combination of open and closed
contacts (5A, 5B, 5C) is interpreted in a decimal manner, with each dry
contact (5A, 5B, 5C) directly corresponds to a set of voltage regulation
parameters (20A, 20B, 20C), such that, when the first contact (5A) is
closed, a first set of parameters (20A) is selected, when the second
contact (5B) is closed, a second set (20B) is selected.

4. The method of claim 2, wherein the combination of open and closed
contacts (5A, 5B, 5C) is interpreted in a binary manner, with each
individual contact (5A, 5B, 5C) corresponding to a bit that can assume
the value 0 when the contact is open or 1 when the contact is closed, the
combination of the several bits composing a binary number that, converted
to a decimal number, indicates which set (20A, 20B, 20C) of voltage
regulation parameters (21) is selected.

5. The method of claim 1 wherein the selection of the set (20A, 20B, 20C)
of voltage regulation parameters (21) is accomplished by programming by
the user, such programming comprising weekdays (22) and time ranges (23,
24) for activating each set (20A, 20B, 20C) of parameters; for each set
of parameters (20A, 20B, 20C) weekdays (22) from Sunday-to Saturday are
selected, as well as a time range defined by an initial hour, minute and
second (23) and a final hour, minute and second (24); when the weekday
indicated by a real-time clock (8) corresponds to one of the weekdays
(22) selected to a given set of parameters (20A, 20B, 20C) and a present
time indicated by the clock (8) is within the time range (23, 24)
selected to the same set of parameters (20A, 20B, 20C), this set of
parameters (20A, 20B, 20C) is then selected for use by the voltage
regulation system (S).

6. A method for voltage regulation, control, protection and monitoring of
state of on-load tap changers of power transformers, voltage regulators,
and capacitor banks wherein a voltage regulation system (S) has two
independent time delay parameters (31L, 31R) available for programming by
a user, wherein one of the delay parameters (31R) is used when a measured
load voltage (13) is below a preprogrammed rated voltage, and the other
delay parameter (31L) is used when the measured load voltage (13) is
above the preprogrammed rated voltage.

7. The method according to claim 6 wherein the voltage regulation system
(S) has several parameters available for user programming of ranges of
voltage deviation (31, 32, 33) in reference to the rated voltage, both
below and above the rated voltage, and for each range of voltage
deviation (31, 32, 33), the voltage regulation system (S) has two
parameters available for user programming of a time delay (21) for OLTC
(15) operation, some of the voltage deviations (31R, 32R, 33R) to be used
when the measured load voltage (13) is too low, below the rated voltage,
and the other (31L, 32L, 33L) to be used when the load voltage (13) is
too high, above the rated voltage; whenever the measured load voltage
(13) is below or above an allowed tolerance margin (30), the voltage
regulation system (S) compares the load voltage (13) to the ranges of
voltage deviation (31, 32, 33), determines which of these ranges of
voltage deviation correspond to measured load voltage (13) and selects a
corresponding time delay parameter (31R, 32R, 33R, 31L, 32L, 33L) to be
effectively used for voltage regulation in system (S) operation.

8. A method for voltage regulation, control, protection and monitoring of
state of on-load tap changers of power transformers, voltage regulators,
and capacitor banks, wherein a voltage regulation system (S) performs
recording of measurements in non-volatile memory (9) according to
parameters programmed by a user comprising: a time interval for periodic
recording; selecting variables (9A) to be recorded in a memory (9),
including: a measured voltage (17), a load voltage (13), a load current
(17') and an OLTC tap position (12), and calculated variables including:
active and reactive power, frequency and load power factor; a recording
mode (9B) for each of the variables (9A) selected for recording, the
recording mode (9B) selected from a group including: instantaneous value
of the variable, average value of the variable calculated during the
interval since last recording, root mean square of the variable
calculated during the interval since last recording, maximum value of the
variable observed during an interval since last recording or minimum
value of the variable observed during the interval since last recording;
and selecting more than one recording mode (9B) for each of the variables
(9A) selected for recording.

9. A method for voltage regulation, control, protection and monitoring of
state of on-load tap changers of power transformers, voltage regulators,
and capacitor banks, wherein a voltage regulation system (S) performs the
OLTC Maintenance Assistant function by measuring an OLTC tap position
measurement through a tap measuring input (12) comprising: counting a
total number of OLTC (15) operations since a beginning of OLTC operation,
the count being increased every time the OLTC tap position measurement
input (12) changes; counting a partial number of OLTC (15) operations
since a last maintenance performed on the OLTC, the counter being
increased every time the OLTC tap position measurement input (12)
changes; wherein both a total counting and a partial counting are
increased by one unit every time the OLTC tap position measurement input
(12) changes, except for tap positions previously selected and programmed
by a user with an specific number to be used to increase both counters;
wherein both the total counting and the partial counting are recorded in
a voltage regulation system (S) non-volatile memory (9); wherein both the
total counting and the partial counting can have values programmed by the
user, so as to allow an application of the OLTC Maintenance Assistant
function with old OLTCs; wherein based on a user programming of a number
of operations after which OLTC maintenance must be performed, the voltage
regulation system (S) issues a warning indicating a need for OLTC
maintenance when a partial operation counting is equal or higher than the
number of operations after which OLTC maintenance must be performed;
wherein the voltage regulation system (S) calculates an average number of
OLTC operations per day by dividing a number of operation in the last X
days by X elapsed days, X being a time interval programmable by the user;
wherein the voltage regulation system (S) calculates a remaining time for
reaching the number of operations for OLTC maintenance, according to a
formula: Y=((No. of operations for maintenance)+(partial operation
counter))/(Average daily operations); wherein the voltage regulation
system (S) issues a maintenance warning indicating that OLTC maintenance
will be necessary within Y days, when a value calculated for Y is equal
or lower than a number of days for advanced maintenance warning
programmed by the user; and wherein the maintenance warnings will remain
active in the voltage regulation system (S) until the user performs a
manual warning reset at a keyboard (3), informing the voltage regulation
system (S) that maintenance has been performed; once the manual reset is
made, partial operation counting since the last maintenance is zeroed and
warnings for maintenance are switched off.

10. The method of claim 9, wherein the voltage regulation system (S)
performs the OLTC Maintenance Assistant function by measuring the OLTC
tap position through the tap measuring input (12) and a load current
(17'), wherein: every time the OLTC (15) tap position measurement input
(12) changes the voltage regulation system (S) squares the load current
measurement and adds the squared value to a previous value in a total
switched current sum recorder since a beginning of the CDC operation,
which is stored in non-volatile memory (9); every time the OLTC (15) tap
position measurement (12) changes the voltage regulation system (S) takes
squares a load current measurement at a time of a tap change and adds the
squared value to the already existing value in the partial switched
current sum recorder since the last maintenance performed on the OLTC
(15), which is stored in non-volatile memory (9) in the voltage
regulation system (S); both the total and the partial recorder can have
its values programmed by the user, so as to allow an application of the
OLTC Maintenance Assistant with old OLTCs; based on a user programming of
a limit value for a sum of switched current after which OLTC (15)
maintenance must be performed, the voltage regulation system (S) issues a
warning indicating a need for OLTC maintenance when the partial sum
recorder is equal or higher than the limit value for maintenance; the
voltage regulation system (S) calculates an average per day increment of
sum of switched current by dividing an increment in a switched current in
a last W days by W elapsed days, W being a time interval programmable by
the user; the voltage regulation system (S) calculates a remaining time
for reaching a limit value of a sum of switched current for OLTC
maintenance, according to: Z=((Sum value for maintenance)+(partial sum
recorder))/(Daily increment average in sum) the voltage regulation system
(S) issues a warning indicating that the OLTC maintenance will be
necessary within Z days, when Z is equal or lower than a number of days
for advanced maintenance warning programmed by the user; and maintenance
warnings will remain active in the voltage regulation system (s) until
the user performs a manual warning reset at a keyboard (3), informing the
voltage regulation system (s) that maintenance has been performed; once a
reset is made, a partial recorder of switched current since the last
maintenance is zeroed and warnings for maintenance are switched off.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. application Ser. No.
12/279,597, filed Aug. 15, 2008, which is a National Phase of
PCT/BR2006/000265, filed Dec. 7, 2006, which is based on Brazilian
Application No. PI 0601093-8, filed Feb. 2, 2006, all of which are herein
incorporated by reference in their entireties.

FIELD OF THE INVENTION

[0002] This invention relates to a "SYSTEM FOR VOLTAGE REGULATION,
CONTROL, PROTECTION AND MONITORING OF STATE OF CHANGERS UNDER POWER
TRANSFORMER LOAD, VOLTAGE REGULATORS, CAPACITOR BANKS AND SIMILAR"
including a voltage regulation system, provided with innovative functions
and features that enable making up for deficiencies of currently used
voltage relays, by preserving unbiased treatment to consumers,
residential or business irrespective of demand curve variations.

BACKGROUND OF THE INVENTION

[0003] Power transformers and autotransformers and voltage regulators are
used in an electric power generation, transmission and distribution
system for power transfer, normally changing the output voltage value in
relation to input. In order to allow controlling voltage supplied to
load, its windings are equipped with taps which are connected to a CDC or
OLTC (On-Load Tap Changer), which makes TAP change used with the
energized transformer and with connected load, changing the coil ratio
and consequently transformer output voltage.

[0004] In order to make the change and tap change the CDC has a motorized
drive mechanism and regulated by signals received in its inputs, to raise
or lower the tap.

[0005] Currently in order to allow automatic voltage regulation supplied
to load, transformers are equipped with a device called automatic voltage
regulator relay, or voltage relay or simply relay, which send to the
changer under load signals to lower or raise the tap position, so as to
keep voltage in the load within programmed limits in relay
parameterization.

[0006] In order to perform the automatic voltage regulation function, the
voltage relays perform the transformer output voltage measuring through a
power transformer (PT) and, the load current through a current
transformer (CT). With these measurements, the voltage relay makes
calculation of the voltage that actually reaches the load, by taking into
consideration voltage drop in the transmission line, proportionate to the
load current. Calculated voltage in load is then compared to a set of
regulation parameters programmed in the voltage relay in order to
determinate when there is need for change in CDC tap. Said parameters
include:

[0007] Rated voltage in load;

[0008] Tolerance margin, which is the allowed voltage percentage over and
under rated voltage;

[0009] Timing for CDC actuating in order to correct voltage, so as to
avoid unnecessary tap change as a result of temporary voltage deviations,
in which actuating time can be constant--regardless of the voltage
deviation magnitude in relation to programmed tolerance margin (linear
timing); or inversely proportional to voltage deviation magnitude in
relation to tolerance margin (inverted timing); and

[0010] Parameters referring to voltage drop in line in a given load
current condition (rated current), allowing the voltage relay to
calculate actual voltage reaching the load.

[0011] Generally current voltage relays also have an input for making CDC
tap position measurement, through a position sensor existing in it.
Measured tap position is then indicated to operator who may also perform
CDC command in manual manner, by blocking automatic voltage regulation
commands. Based on this CDC tap position measurements, some existing
voltage relays also perform CDC control in transformers electrically
connected in parallel, therefore using the concept called Master-Command
or Master-Follower. In this concept, one of the transformers in parallel
is selected in master mode and the other in commanded mode. Every tap
change performed by the master must be repeated by followers that lose
their command independence to simply obey master transformer tap changes.
In this way, all transformers will be in the same tap position, which
prevents current circulation among windings in parallel, sending new trap
change commands is blocked, preventing tap difference between
transformers from increasing. 14) In operation in parallel of transformer
banks consisting of individual single-phase transformers, additional care
must be taken in order to ensure that the three single-phase transformers
of which a bank consists are with their CDCs in the same tap position, in
order to prevent a voltage unbalance between the three-phase system
phases. To this end a synchronism, check is performed between tap
positions of the three single-phase transformers of the same bank,
blocking CDC operation and issuing an alarm is any tap discrepancy occurs
between the bank phases. For maintenance and testing purposes only, when
the bank is not electrically connected in parallel to others, is when
CDCs of each phase can be operated in different tap positions. In order
to allow these tests and maintenances in existing system will have a
selection, manually performed by the operator, where it is indicated
whether the three transformers of the same bank must operate in the same
tap position ("bank" mode) or in individual manner ("individual phase"
mode).

STATE OF THE ART DISADVANTAGES

[0012] One of the limitations of existing voltage relays is related to
transformers serving consumers in different load profiles, such as
residential, business and industrial consumers. In these cases there may
be prevalence of a certain type of consumer on certain weekdays or times
and, of another type of consumer in other periods of the week. In this
way, ideal parameter settings for a type of consumer may be totally
unsuitable for another type of consumer. With currently available voltage
relays there is no satisfactory solution for this occurrence, forcing the
operator to favor a certain type of consumer in detriment of another or,
then make periodic manual changes to the voltage relay parameter
settings.

[0013] In conventional voltage relays used in transformers, one
of the programmed parameters for making the voltage regulation is to
delay CDC operation in order to correct voltage that, has as a function
preventing unnecessary tap changes is important due to the fact that the
CDC is the equipment that generates the highest maintenance costs in
transformers and, the need for maintenance in the CD is basically
determined by the number of trap changes made. Accordingly, in order to
reduce the changer maintenance costs the ideal is to make the highest
possible timing adjustment. On the other hand, maximum times that loads
may remain in voltages over or below tolerance limits are often
determined by the electric sector regulatory agencies that, may establish
different times for voltage below or over tolerance. In this context,
conventional voltage relays are fitted with a single timing adjustment
used both when there is need to increase voltage and when it is necessary
to decrease voltage. This fact forces the operator to adjust timing
according to the shortest time defined by regulatory agencies (between
allowed times for a voltage below or over tolerance), which results in
additional CDC actuations in a condition that a longer operation time
would be allowed.

[0014] In currently used voltage relays in
transformers, when voltage in the lead exceeds lower and upper limits
defined by programmed tolerance margin timing count is started for CDC
operation. Said timing may be a linear type, in which actuation time is
constant, regardless of the voltage deviation magnitude in relation to
programmed tolerance margin, or reverse type timing, in which actuation
time is inversely proportional to voltage deviation magnitude in relation
to the tolerance margin. As already mentioned, timing settings are based
on maximum times in which loads may remain with voltages over or below
tolerance limits, and said times are often determined by the electric
sector regulatory agencies, which, generally, determine shorter times as
voltage deviation increases over or below allowed tolerance limit.
Accordingly, conventional relays have as the only feature meeting the
needs of shorter timings for higher voltage deviations than reverse
timing. This forces the operator to adjust timing in order to meet or
exceed arbitrarily defined times by the regulatory agency, which usually
tends to cause unnecessary additional CDC actuations when adjustment made
takes a shorter actuation time than required by the regulatory agency.

[0015] On-Load Tap Changers (CDC) are equipped with a motorized drive
mechanism that receives command signals to increase or decrease the tap
position. Such drive has intern ally several control elements, such as,
relays, mechanically driven end of line switches, among so many other
elements. Certain failures in referred control elements can lead the CDC
to make unsolicited tap changes, which may be repeated in successive
manner leading the CDC to reach an extreme upper or lower position,
causing either too high or too voltage values in the load. The occurrence
of this type of occurrence is highly undesirable by consequences that may
be, for example, load shutoff by its protection actuation or even damages
in loads.

[0016] Following the same above-mentioned context, of the
Changers (CDCs) motorized drive mechanism, certain failures may lead the
CDC not to make requested tap changes by the voltage regulation system,
which may lead voltage in the load to slowly vary as load current and
primary voltage in transformer are changed. After some time, voltage in
load may reach very high or very low due to lack of voltage correction
that would be provided by CDC operation, with consequences that may go
from load shutoff by actuation of its protections or even damages in
load. Accordingly, in conventional relays, inoperative CDC condition is
only perceived after some time, when voltage reaches too high or too
values, already with damage to the load.

[0017] Several researches
conducted around the world referring to failures and stoppages for
maintenance in transforms clearly signal that the CDC is the equipment
that generates the highest failures rates and maintenance costs in
transformers, the need for maintenance in the CDC being basically
determined by the number of tap changes made by it. Currently, CDCs are
equipped with mechanical operation counters that record the number of tap
changes made since the equipment operation start, control of this number
of operations being made by maintenance personnel, which in a certain
frequency moves to the CDC and writes down the number of operations at
that time. With this information inspection and/or maintenance need is
determined in the CDC, having as a parameter the number of operations
since the last inspection/maintenance if the value recommended by
manufacturer is reached.

[0018] Following above-commented research, in
relation to CDCs, the need for maintenance in the latter is also
determined by the wear and tear of contacts that make electric arc
interruption during tap change. As is known by technicians in the matter,
the wear of said contacts is proportional to the sum of interrupted
current squares. Currently, maintenance in CDCs is focused on their
number of operations, which opens the possibility of problems appearing
in CDCs, if interrupted currents by their contacts have sufficient
intensity to cause excessive contact wear, anticipating the number of
operations predicted for maintenance. Additionally, maintenances simply
based on CDC operations, statistically reveal that maintenance could have
been postponed for some time, taking into account that changer contacts
are found in good state.

[0019] In conventional relays in which
operations control is done in parallel of transformers by the
Master-Commanded method it is necessary to select for each transformer
its function in master parallelism control, commanded or further
individual (if transformer is not operating in parallel with any other).
Bu the Master-Commanded concept, only one of transformers can be selected
as master and there may not be transformers selected as Commanded if
there is no Master transformer. This enables making invalid
configurations for parallelism control in existing voltage relays, such
as, for example, the selection of more than one transformer as master or
selection of transformers as commanded without the existence of a master.

[0020] In existing voltage relays where operation control is made in
parallel of transformers by the Master-Commanded method, the voltage
relay makes synchronism verification taps of transformers in parallel,
blocking CDC operation and issuing an alarm if there is tap discrepancy.
However, in the condition in which transformers are not in parallel and,
therefore are selected for operating in individual mode, there is no
obligation for their tap positions to be equal. However, at any time it
may be necessary for said transformers having to be operated in parallel
and, to this end of them will have to be selected as mater and the others
as commanded. It may occur that master-commanded selections will be made
with transformer CDCs in different tap positions, which will lead the
voltage relay to issue a tap discrepancy alarm between CDCs.

[0021] For
two or more transformers to be electrically connected in parallel it is
necessary for their CDCs to be in the same tap position, so as to prevent
current circulation among windings. Establishing the electric connection
of transformer windings in parallel is usually done by closing a
substation circuit breaker that can only be closed after transformer CDCs
are in the same tap position. Currently this verification is manually
made by the operator, therefore, being subject to human failure.

[0022]
In conventional relays where operation control in parallel of transformer
banks consisting of single-phase transformers is done, it is necessary to
ensure, during normal operation, that the three single-phase transformers
of which a bank consists are with their CDCs in the same tap position.
However, in order to allow testing and maintenances existing systems have
a selection where it is indicated whether the three transformers of the
same bank should operate in the same tap position ("bank" mode) or in
individual manner ("individual phase" mode). This selection is made
manually, which opens the possibility for an operator error, which may
select the transformer CDC of each phase to operate in individual manner,
and consequently in different tap position from the other phases, even if
the transformer bank is in normal operation electrically connected in
parallel to other banks.

[0023] In existing systems where operation
control in parallel of transformer banks consisting of single-phase
transformers is done, a synchronism checking is made between tap
positions of the three single-phase transformers of the same bank,
blocking CDC operation and issuing an alarm if a tap discrepancy occurs
between the bank phases. However, in the condition that the bank is in
maintenance and its phases are in "individual phase" mode, there is no
obligation for their tap positions to be equal. At any time, however, it
may be required for the bank to return to operate normally, and to this
end the phases should be changed to "bank" mode. This opens the
possibility for phase selections to "bank:" mode to be made with the
three phases of transformers in different tap positions, which will lead
voltage relay to issue a tap discrepancy alarm between CDCs.

SUMMARY OF THE INVENTION

[0024] Thinking about the above-commented inconveniences, the inventor, a
person working in the electric power sector, has created the system in
question that comes to make more reliable voltage regulation, protection
and state if changers under equipment load state monitoring, such as,
power transformers and voltage regulators, making up for deficiencies of
current relays that perform voltage regulation based on a single set of
parameters; the other way about, proposed invention provides
pre-programming for different voltage regulation parameter settings, each
setting being suitable to a given prevailing load condition, allowing
consumer service with different load profiles, having to this end several
regulation parameters, adjustable in independent manner.

[0025] Furthermore, the proposed system allows selection of the voltage
regulation parameter set made by dry contacts where a combination of open
and closed contacts is used indicative of the parameter set that must be
used in voltage regulation. In continuity, the claimed system allows
voltage regulation parameter set selection to be made by daily and hourly
programming, in addition to other temporary parameters. Another
innovation of the proposed system is the possibility of independent value
adjustment of CDC actuation timing for conditions in which voltage is
over or below allowed tolerance margins. Proposed system also allows
adjustment of several voltage deviation ranges, different CDC actuation
times being associated with each deviation range. The system also has a
mass memory function (non-volatile), where measurement values made by the
system are recorded obeying the interval programmed by the operator,
having several innovating features. In conformity with the new invention
it is possible to block the erroneously tripped CDC, equally with several
features to be discussed later. Such as mentioned above the system has
the function of detecting the inoperative CDC, before voltage reaches
extreme values also meeting several features. In this same line, the
system proposed herein has the innovating function of CDC maintenance
assistant, with several features oriented toward statistical maintenance
control of changers under load. Another new system function is the
"Master-Commanded-Individual" smart selection programming, when there is
an operation in parallel of several transformers, and "Bank-Individual
Phase" smart programming, when using banks consisting of three
independent single-phase transformers, preventing several inconveniences
of existing systems. At last the proposed system has the synchronism
signaling function and correct programming, which automates the tap
synchronism checking process when electrically connecting transformers in
parallel, which prevents human failures in this checking.

[0026] The proposed invention prevents, in proposed voltage regulation
system parameterization, the operator from being forced to privilege a
certain consumer in detriment of others or then having to make periodical
manual changes to voltage relay parameter settings.

[0027] Allow that, by means of dry contacts, it will be possible to select
a set of voltage regulation parameters, at a distance, by using, for
example, selection switches within operator reach in the control room or
further output contacts of remote terminal units (RTUs);

[0028] By the selection of voltage regulation parameter set through daily
and hourly programming, allow the operator to program the voltage
regulation system to automatically adapt it to prevailing conditions of
load profiles subject to hourly, daily and weekly variations.

[0029] By timing setting programming for independent CDC actuation in the
event that voltage is over or below allowed tolerance margins, giving
conditions for meeting the regulatory agency requirements in relation to
allowed times for voltage off tolerance, at the same time as reducing to
the maximum possible the number of CDC operations, reducing maintenance
costs.

[0030] By programming settings for several voltage deviation ranges, each
associated deviation range being different CDC actuation times (one time
adjustment to increase voltage and one adjustment to reduce voltage),
conditions are given for the user to create a customized timing mode, in
which operation time diminishes exactly as desired as voltage deviation
increases, so as to exactly meet the regulatory agency requirements in
relation to allowed times for voltage off tolerance, at the same time as
reducing to the maximum possible the number of CDC operations, reducing
maintenance costs.

[0031] By the mass memory function, allows the operator to choose for
recording in the memory only variables he considers important, avoiding
spending memory space with unnecessary variables for their application.

[0032] Still by the mass memory function, the operator may choose to
record not only the variable instantaneous value, but also minimum,
maximum, arithmetic mean or square variable mean values during the time
interval since the last made recording. With that it becomes possible to
retrieve, from data in memory, the electric system behavior (for example,
maximum, minimum, average voltages, etc.) and analyze tension regulation
efficiency.

[0033] By the tripped CDC blocking function, preventing the occurrence of
serious undervoltages or overvoltages that may cause forced transformer
switching off or damage to loads connected to it.

[0034] The "CDC maintenance assistant" function allows:

[0035]
Automating CDC control and number of operations, reducing costs related
to traveling to the equipment just to check the current number of
operations in mechanical command;

[0039]
Working in conjunction, the several above-listed benefits may allow
failures rate reduction in CDCs, due to interval adjustment and CDC
maintenance quality improvement, taking into consideration that
maintenance personnel have their time freed for better preparation for
the activity. Additionally, the "CDC maintenance assistant" function
allows:

[0040] Making the CDC maintenance philosophy transition of maintenance
based on time for maintenance modeled on the state of the equipment,
avoiding unnecessary CDC interventions and, consequently, reducing
maintenance costs:

CDC failure risk reduction due to excessive wear of arc interruption
contacts; In order to prevent unnecessary CDC interventions, it reduces
the risk of problems caused in it by human failures when intervening for
maintenance: With the maintenance warning issued in advance by the
voltage regulation system, maintenances can be prepared in advance to
become effective at the ideal time only, preventing excessive delays in
maintenances caused by lack of materials and/or lack of logistics
preparation for jobs: Working in conjunction, the several above-listed
benefits may allow failures rate reduction in CDCs, due to knowing the
actual state of arc interruption contacts. Furthermore, it improves CDC
maintenance quality, since when preventing unnecessary interventions in
CDC, maintenance professionals have their time freed for better
preparation for the activity.

[0041] By the smart master-commanded-individual programming, all
possibilities for the operator making invalid programming are inhibited,
such as more than one transformer as a master, or the existence of
commanded transformers without there being a master, or further selecting
a transformer as commanded without its tap position being equal to the
mater, among other invalid programming possibilities.

[0042] By smart "individual bank-phase" programming, possibilities for the
operator making invalid programming are inhibited, such as selecting that
the transformer CDC of each phase will operate in individual manner, and
consequently in different tap position from the other phases, even if the
that transformer bank is in normal operation and electrically connected
in parallel to other banks, among other invalid programming
possibilities.

[0043] By the "correct synchronism and programming signaling" function",
preventing the operator from making the mistake of electrically
connecting in parallel transformers that are not found in the same tap
position.

[0044] Next, the invention will be technically explained, by using as a
basis block diagrams.

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0045] FIG. 1 is a schematic of a voltage regulation system according to
one embodiment of the present invention.

[0046] FIG. 2 is schematic showing parameter sets according to one
embodiment of the present invention.

[0047] FIG. 3 is a schematic illustrating voltage deviation parameters
according to one embodiment of the present invention.

[0048] FIG. 4 is a schematic representing a non-volatile memory used in
some embodiments of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

[0049] The present invention preferably applies to power transformers (1)
and voltage regulators and similar, it being that this system (S)
hereinafter referred to as voltage regulation system, by means of a
microprocessor (2) provides innovating functions that make up for
deficiencies of currently existing voltage relays, highlighting
pre-programming, by means of man-machine interface such as, for example,
keyboard and display (3), or serial communication (4) of several settings
and different voltage regulation parameters, each adequate setting for a
certain prevailing load condition, performed by means of dry contact
inputs (5), contact outputs (6) being destined for self-diagnosis
signaling and alarms (7). Voltage regulation allows parameter selection
to be made by means of daily and hourly programming through an internal
clock (8). Said system (S) also has the non-volatile memory function (9);
CDC blocking function (10) that directly acts on the motorized drive (11)
of the CDC; tap position measurement (12) with inoperative CDC detection
or release, CDC maintenance assistant; smart programming and correct
synchronism and correct programming function (7).

[0050] As already commented, transformers (1) are used in electric power
generation, transmission and distribution, usually changing the output
voltage value for load (13) in relation to input voltage (14). This is
done with windings equipped with taps connected to an Onload Tap Changer
(CDC) (15) that makes tap change with the energized transformer (1) and
connected load. Therefore the CDC has a motorized drive mechanism (11)
that obeys input signals to raise and lower the tap (10). In order to
perform the voltage regulation function, an output voltage measurement is
made (17) by means of a power (PT) and current transformer (17') of load
by means of a current transformer (CT), more particularly, proposed
regulation system (S) consists of a microprocessor (2) that with said
voltage and current measurements (17 and 17') provides new functions and
features, making up for deficiencies of currently existing relays that
make voltage regulation base on a single parameter set; unlike the
applied for system (S) that allows them to be pre-programmed by a
man-machine interface such as, for example a keyboard and display (3), or
a serial communication (4) several settings for voltage regulation
parameters, each setting being adequate for a given prevailing load
condition that may be identified by the time informed by the internal
clock (8). In order to enable this function, the system (S) proposed
herein has six or more regulation parameter sets adjustable in
independent manner, each set having the parameters described below:

[0053] Timing adjustment for CDC actuation in order to correct voltage;

[0054] Choice of linear or reverse timing type;

[0055] Parameters referring to voltage drops in the line:

[0056] As already mentioned, the voltage regulation system allows
selection of the voltage regulation parameter set used in the system
operation to be made by means of daily and hourly programming, consisting
of the weekdays and time ranges for activating parameter set. For each
parameters weekdays (Sunday through Saturday) are selected, in addition
to the time range defined by start hour, minute and second, range end
hour, minute and second. Within the days and time range selected for a
given set it will be used for voltage regulation. In other words, based
on its real-time internal clock (8) that keeps day, month, year, weekday,
hour, minute and second information and based on performed daily and
hourly programming the voltage regulation system makes the choice of the
regulation set to be used at current time.

[0057] In addition to regulation parameter set selection through a
daily/hourly programming, this selection can be made by dry contact input
(5). The combination of open and closed contacts in these inputs
indicates to the voltage regulation system which parameter set must be
used. The combination of open and closed contacts in these inputs can be
encoded in decimal manner, that is, each parameter set directly
corresponds to an input contact, or can be encoded in binary manner, with
the combination of input contact states forming a number corresponding to
the respective parameter set.

[0058] The proposed voltage regulation system allows independent CDC
timing and performance values to be adjusted for conditions in which
voltage is over or below allowed tolerance margins, providing conditions
for meeting the sector regulatory agency requirements in relation to
allowed times for voltage off tolerance, at the same time as CDC
operation time is reduced to the maximum possible, reducing maintenance
costs.

[0059] Another proposed system innovation is the adjustment, in addition
to the tolerance margin, of several voltage deviation ranges, it being
that each deviation range is associated with different CDC operation
times (for each deviation range one time setting for increasing voltage
and one setting for reducing voltage).

[0060] Such a fact allows the operator to create a customized timing mode,
in which operation time diminishes exactly as desired as voltage
deviation increases, so as to exactly meet the regulatory agency
requirements in relation to allowed times for voltage off tolerance, at
the same time as CDC operation time is reduced to the maximum possible,
reducing maintenance costs.

[0061] The regulation system proposed herein The system also has the mass
memory function, where they are recorded in a non-volatile memory (9),
obeying the interval programmed by the operator, measurement values made
by the system, it being that this function has the following features:

[0062] Variables to be recorded can be freely chosen by the operator among
all measures or calculated values by the system, such as, measured
voltage in transformer, voltage in load, load current, powers, frequency,
power factor, CDC tap position, etc.

[0063] For each variable selected for recording by the operator the
recording mode can be chosen among the options: instant value (measured
value at recording time), arithmetic mean of measurements made since the
last recording in memory, square mean of measurements made since the last
recording in memory or minimum value of measurements made since the last
recording in memory.

[0064] One and the same measurement can be selected for recording in
memory in several different modes. For example, "voltage in load"
variable can be selected for recording with instant value, mean value,
maximum value and also minimum value.

[0065] In order to prevent certain failures in CDCs the proposed voltage
regulation system has the "tripped CDC blocking" function, with the
following features:

[0066] Performance by the voltage regulation system of CDC tap position
measurement (12);

[0067] It considers normal CDC operation the condition in which the
voltage regulation system issues a signal to the CDC to raise or lower
tap position (10) and after that the CDC tap position undergoes a change
in the same direction of sent signal (raise or lower the tap);

[0068] It considers that the CDC is tripped if a change in measured CDC
tap (12) occurs without the voltage regulation system having previously
sent a signal (10) requesting this change, or further if the voltage
regulation system issues a signal for tap change (10) and the CDC makes a
change in the opposite direction to issued signal. In this case an output
contact (6) can be programmed by the operator for remote signaling (7) of
the occurrence;

[0069] In order to prevent false tripped CDC alarms, due, for example, to
tap changes manually requested by the operator directly on the motorized
drive panel, it may be programmed in the voltage regulation system to
only consider that the CDC is tripped if several successive tap changes
occur, being the number of tap changes for considering that the CDC is
tripped programmed by the operator;

[0070] A tripped CDC situation is detected, as described above, an output
contact (10) is activated in the voltage regulation system. This contact
can be connected by the operator in order to switch off the CDC drive
motor supply (11), forcing him in this manner to stop tap changes and
avoid the consequences such as forced transformer switching off or damage
to the load.

[0071] In order to allow quick detection of an inoperative changer, before
voltage reaches too high or two low values, the voltage regulation system
proposed herein has the "Inoperative CDC detection" function with the
following features:

[0072] Performance by the voltage regulation system of CDC tap position
measurement (12);

[0073] It considers that the CDC is found in normal condition if the
voltage regulation system issues a signal (10) to the CDC to raise or
lower tap position and after that the CDC tap position undergoes a change
in the same direction of sent signal (raise or lower the tap, detected by
the CDC position measurement) within the time period programmed by the
operator:

[0074] It considers that the CDC is inoperative if the voltage regulation
system issues a signal (10) to the CDC to raise or lower tap position
and, after that the CDC tap position does not undergo a change within the
time period programmed by the operator (the change is detected by
measuring the CDC position);

[0075] In order to avoid false inoperative CDC alarms, such as, for
example, during maintenances in which the CDC is kept inoperative, the
operator may enable or disable this function in the voltage regulation
system;

[0076] When detecting the inoperative CDC situation, as described above,
the condition is signaled through an alarm indication in the voltage
regulation system that, may also activate an output contact (6) for
remote alarm indication (7);

[0077] The alarm indication will remain active in the voltage regulation
system and the alarm contact will remain activated until the operator
makes a manual alarm reset informing to the system voltage regulation
system that he is already aware of the problem.

[0078] The operator may also enable the voltage regulation system to make
an automatic inoperative CDC alarm reset, the automatic reset being made
as soon as new CDC tap change attempt is successively made.

[0079] A new function of the proposed voltage regulation system is of CDC
Maintenance Assistant, with the following features:

[0080] Total CDC operation number count, since the beginning of its
operation, by measuring the CDC position (12). Every time the measured
tap position changes the CDC operation counter increases the number of
required operations for making referred tap change (one operation in most
cases, there may also be several operations in case of CDCs with
intermediate positions);

[0081] Partial CDC operation number count since the last inspection or
maintenance made by the operator, by measuring the CDC position (12), in
similar manner to above-described total operation number count:

[0082] Initial operation numbers of both counters (total and partial)
adjustable by the operator, allowing utilization of the CDC, also in old
equipment, in addition to allowing operation count correction in the
event of a failure in the voltage regulation system.

[0083] A warning indicating that the operation number for CDC maintenance
when partial operation count (since the last maintenance) has exceeded
the number of operations for maintenance adjusted by the operator; with
the possibility of programming an output relay (6) for remote signaling
(7);

[0084] CDC average daily operation count, made by dividing the sum of
total operation number in the last X days by the number of X days, X
being a time window programmable by the operator between one and three
hundred and sixty five days;

[0085] Approximate Y remaining time calculation for reaching the number of
operations for maintenance, according to the ratio below:

[0086] Warning indication that the number of operations for CDC
maintenance will be reached within Y days, when remaining time
calculation for Y maintenance is lower than the number of advance days
for maintenance warning adjusted by the operator between zero and three
hundred and sixty five days, with the possibility of programming an
output relay (6) for remote signaling (7);

[0087] The maintenance warning indication will remain active in the
voltage regulation system and the alarm contact(s) will remain activated
until the operator makes a manual warning reset, informing the voltage
regulation system that maintenance has already been performed. Once the
reset is made, partial operation count since the last maintenance is
zeroed and warnings are switched off for maintenance.

[0088] In addition to the above-listed the "CDC maintenance assistant",
has further the following features:

[0089] Every time a CDC tap change is made, detected by the tap
measurement means (12), the voltage regulation system the load current
measurement (17') at the time of tap change and raises it to the power of
2. Obtained value is added to the already existing one in the total
changed current sum recorder since the beginning of the CDC operation,
which is kept in a non-volatile memory in the voltage regulation system;

[0090] As described above, every time a CDC tap change is made, detected
by means of tap measurement (12), the voltage regulation system takes the
load current measurement (17') at the time of the change and raises it to
square. Obtained value is also added to the already existing value in
another recorder, this one dedicated to the sum of partial change current
since the last CDC maintenance, which is kept in the voltage regulation
system non-volatile memory;

[0091] Initial values of both changed current sum records (total and
partial) adjustable by the operator, allowing using the CDC maintenance
assistant also in old equipment, in addition to allowing sum corrections
in the event of a failure in the voltage regulation system;

[0092] A warning indication that the changed current sum for CDC
maintenance has been reached when the partial sum record (since the last
maintenance) exceeds the sum value for maintenance adjusted by the user,
with the possibility of output relay (5e) programming for remote
signaling (7);

[0093] Daily increment average calculation in the current sum changed by
the CDC, made by dividing the increment in the current sum in the last W
days by W number of days, W being a time window programmable by the
operator between one and three hundred and sixty five days;

[0094] Approximate remaining time Z calculation for reaching sum value for
maintenance, according to the formula:

[0095] A warning indication that the number of operations for CDC
maintenance will be reached within Z days, when remaining time for
maintenance Z calculation is lower than the number of advance days for
maintenance warning adjusted by user between zero and three hundred and
sixty five days, having the possibility of programming the output relay
(6) for remote signaling (7);

[0096] The maintenance warning indication remains active in the voltage
regulation system and alarm contact(s) will remain activated until user
makes manual warning reset, informing the voltage regulation system that
maintenance has already been performed, Once this reset is made, the
partial sum recorder of changed currents since the last maintenance is
zeroed and maintenance warnings are switched off.

[0097] Proposed system also performs the "smart
master-commanded-individual programming" function, with the following
features:

[0098] Inhibiting the possibility of selecting any transformer as master
if there is already any other transformer selected as master. In this
event in which there is already a selected master, all other transformers
can only be selected as commanded or individual;

[0099] Inhibiting the possibility of selecting any transformer as
commanded if there is not yet a transformer selected as master. In this
event, in which there is not yet a selected master, all other
transformers can only be selected as master or individual;

[0100] Inhibiting the possibility of changing the programming of the
transformer selected as master to commanded or individual if there is one
or more transformers selected as commanded, in the way avoiding that
there will be transformers in commanded without there being a master.

[0101] In addition to what has already been commented above, the "smart
master-commanded-individual programming" function has as features, in
addition to those already mentioned:

[0102] Rejecting the selection change of any transformer from individual
mode to commanded mode if its measured tap position (12) is not equal to
a master transformer one, avoiding thereby unnecessary alarm issuing due
to tap discrepancy;

[0103] If it is insisted in the attempt to program a transformer as
commanded without its measured tap position (12) being equal to a master
transformer one, in addition to rejecting this programming the voltage
regulation system will issue an "invalid parallelism programming" alarm,
warning the operator about the situation, with output relay programming
possibility (6) for remote signaling (7);

[0104] Proposed system also performs the "smart bank-individual phase
programming" function, with the following features:

[0105] Inhibiting the possibility of selecting any phase of a single-phase
transformer bank for operation in the "individual phase" mode if the bank
is selected for operation in parallel with other banks, that is, if the
bank is selected in master or commanded mode.

[0106] Inhibiting the possibility of selecting any phase of a single-phase
transformer bank for operation in the "individual phase" mode if the bank
is selected for operation in automatic mode, that is, with CDCs being
controlled according to load voltage and current measurements.

[0107] Only allowing selecting one of the phases of a single-phase
transformer bank for operation in "individual phase" mode if the bank is
selected for operation in individual and manual mode.

[0108] Automatically changing any phase of a single-phase transformer bank
that is selected for operation in "individual phase" mode to "bank" mode
if the bank is selected for operation in master, commanded or automatic
mode.

[0109] In addition to what has already been commented above, the "smart
bank-individual phase programming" function has as features, in addition
to those already mentioned:

[0110] Rejecting the selection change of any phase of a transformer from
"individual phase" mode to "bank" mode if its tap position is not equal
to phase A one, adopted as a reference, avoiding thereby unnecessary
alarm issuing due to tap discrepancy. If it is insisted in the attempt to
program a phase in the "bank" mode transformer without its tap position
being equal to phase A one, in addition to rejecting this programming the
voltage regulation system will issue an "invalid parallelism programming"
alarm, warning the operator about the situation:

[0111] Proposed system also performs the "correct synchronism and
programming signaling" function, with the following features:

[0112] In transformers selected in individual mode no correct synchronism
and programming signaling is issued (since there is no, in this case,
commitment to keep tap position equal to master transformer position):

[0113] In each transformer selected in commanded mode it is signaled that
synchronism and programming are correct only if transformer tap position
(12) is equal to master tap position and if current individual
master-commanded situation is valid (there is only one master
transformer);

[0114] In selected transformer is master mode it is always signaled that
synchronism and programming are correct, because tap position of this
transformer as taken as a reference for selected transformers as
commanded and is considered correct by default.

[0115] The main usefulness of the above-mentioned function, with
above-described features is to serve as a permission signal for closing
the circuit breaker that connects the winding of each transformer in
parallel with the other, allowing automating the synchronism check
function before connection in parallel, which is currently done in manual
manner. To that end, correct synchronism and programming signaling can be
made by means of a serial communication network (4) or further by
activating an output contact (6) for each transformer.